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                        自述
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                            <b>1.</b>
                        
                        介绍
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                            <b>1.1.</b>
                        
                        动机
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                            <b>1.2.</b>
                        
                        核心概念
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                            <b>1.3.</b>
                        
                        三大原则
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                            <b>1.4.</b>
                        
                        先前技术
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                            <b>1.5.</b>
                        
                        生态系统
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                            <b>1.6.</b>
                        
                        示例
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                            <b>2.</b>
                        
                        基础
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                            <b>2.1.</b>
                        
                        Action
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                            <b>2.2.</b>
                        
                        Reducer
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                            <b>2.3.</b>
                        
                        Store
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                            <b>2.4.</b>
                        
                        数据流
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                            <b>2.5.</b>
                        
                        搭配 React
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                            <b>2.6.</b>
                        
                        示例：Todo List
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                            <b>3.</b>
                        
                        高级
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                            <b>3.1.</b>
                        
                        异步 Action
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                            <b>3.2.</b>
                        
                        异步数据流
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                            <b>3.3.</b>
                        
                        Middleware
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                            <b>3.4.</b>
                        
                        搭配 React Router
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                            <b>3.5.</b>
                        
                        示例：Reddit API
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                            <b>3.6.</b>
                        
                        下一步
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                            <b>4.</b>
                        
                        技巧
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                            <b>4.1.</b>
                        
                        迁移到 Redux
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                            <b>4.2.</b>
                        
                        使用对象展开运算符
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                            <b>4.3.</b>
                        
                        减少样板代码
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                            <b>4.4.</b>
                        
                        服务端渲染
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                            <b>4.5.</b>
                        
                        编写测试
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                            <b>4.6.</b>
                        
                        计算衍生数据
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                            <b>4.7.</b>
                        
                        实现撤销重做
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                            <b>4.8.</b>
                        
                        子应用隔离
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                            <b>4.9.</b>
                        
                        组织 Reducer
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                            <b>4.9.1.</b>
                        
                        Reducer 基础概念
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                            <b>4.9.2.</b>
                        
                        Reducer 基础结构
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        <li class="chapter " data-level="4.9.3" data-path="docs/recipes/reducers/SplittingReducerLogic.html">
            
                
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                            <b>4.9.3.</b>
                        
                        Reducer 逻辑拆分
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        <li class="chapter " data-level="4.9.4" data-path="docs/recipes/reducers/RefactoringReducersExample.html">
            
                
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                            <b>4.9.4.</b>
                        
                        Reducer 重构示例
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                            <b>4.9.5.</b>
                        
                        `combineReducers` 用法
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        <li class="chapter " data-level="4.9.6" data-path="docs/recipes/reducers/BeyondCombineReducers.html">
            
                
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                            <b>4.9.6.</b>
                        
                        `combineReducers` 进阶
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        <li class="chapter " data-level="4.9.7" data-path="docs/recipes/reducers/NormalizingStateShape.html">
            
                
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                            <b>4.9.7.</b>
                        
                        State 范式化
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        <li class="chapter " data-level="4.9.8" data-path="docs/recipes/reducers/UpdatingNormalizedData.html">
            
                
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                            <b>4.9.8.</b>
                        
                        管理范式化数据
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        <li class="chapter " data-level="4.9.9" data-path="docs/recipes/reducers/ReusingReducerLogic.html">
            
                
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                            <b>4.9.9.</b>
                        
                        Reducer 逻辑复用
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        <li class="chapter " data-level="4.9.10" data-path="docs/recipes/reducers/ImmutableUpdatePatterns.html">
            
                
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                            <b>4.9.10.</b>
                        
                        不可变更新模式
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        <li class="chapter active" data-level="4.9.11" data-path="docs/recipes/reducers/InitializingState.html">
            
                
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                            <b>4.9.11.</b>
                        
                        初始化 State
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        <li class="chapter " data-level="5" data-path="docs/FAQ.html">
            
                
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                            <b>5.</b>
                        
                        常见问题
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        <li class="chapter " data-level="5.1" data-path="docs/faq/General.html">
            
                
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                            <b>5.1.</b>
                        
                        综合
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        <li class="chapter " data-level="5.2" data-path="docs/faq/Reducers.html">
            
                
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                            <b>5.2.</b>
                        
                        Reducer
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        <li class="chapter " data-level="5.3" data-path="docs/faq/OrganizingState.html">
            
                
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                            <b>5.3.</b>
                        
                        组织 State
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        <li class="chapter " data-level="5.4" data-path="docs/faq/StoreSetup.html">
            
                
                    <a href="../../../docs/faq/StoreSetup.html">
                
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                            <b>5.4.</b>
                        
                        创建 Store
                    </a>
            
            
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        <li class="chapter " data-level="5.5" data-path="docs/faq/Actions.html">
            
                
                    <a href="../../../docs/faq/Actions.html">
                
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                            <b>5.5.</b>
                        
                        Action
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        <li class="chapter " data-level="5.6" data-path="docs/faq/CodeStructure.html">
            
                
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                            <b>5.6.</b>
                        
                        代码结构
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        <li class="chapter " data-level="5.7" data-path="docs/faq/Performance.html">
            
                
                    <a href="../../../docs/faq/Performance.html">
                
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                            <b>5.7.</b>
                        
                        性能
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        <li class="chapter " data-level="5.8" data-path="docs/faq/ReactRedux.html">
            
                
                    <a href="../../../docs/faq/ReactRedux.html">
                
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                            <b>5.8.</b>
                        
                        React Redux
                    </a>
            
            
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        <li class="chapter " data-level="5.9" data-path="docs/faq/Miscellaneous.html">
            
                
                    <a href="../../../docs/faq/Miscellaneous.html">
                
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                            <b>5.9.</b>
                        
                        其它
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            </ul>
            
        </li>
    
        <li class="chapter " data-level="6" data-path="docs/Troubleshooting.html">
            
                
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                            <b>6.</b>
                        
                        排错
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        <li class="chapter " data-level="7" data-path="docs/Glossary.html">
            
                
                    <a href="../../../docs/Glossary.html">
                
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                            <b>7.</b>
                        
                        词汇表
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        <li class="chapter " data-level="8" data-path="docs/api/index.html">
            
                
                    <a href="../../../docs/api/index.html">
                
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                            <b>8.</b>
                        
                        API 文档
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            <ul class="articles">
                
    
        <li class="chapter " data-level="8.1" data-path="docs/api/createStore.html">
            
                
                    <a href="../../../docs/api/createStore.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.1.</b>
                        
                        createStore
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.2" data-path="docs/api/Store.html">
            
                
                    <a href="../../../docs/api/Store.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.2.</b>
                        
                        Store
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        </li>
    
        <li class="chapter " data-level="8.3" data-path="docs/api/combineReducers.html">
            
                
                    <a href="../../../docs/api/combineReducers.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.3.</b>
                        
                        combineReducers
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.4" data-path="docs/api/applyMiddleware.html">
            
                
                    <a href="../../../docs/api/applyMiddleware.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.4.</b>
                        
                        applyMiddleware
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.5" data-path="docs/api/bindActionCreators.html">
            
                
                    <a href="../../../docs/api/bindActionCreators.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.5.</b>
                        
                        bindActionCreators
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.6" data-path="docs/api/compose.html">
            
                
                    <a href="../../../docs/api/compose.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.6.</b>
                        
                        compose
                    </a>
            
            
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            </ul>
            
        </li>
    
        <li class="chapter " data-level="9" data-path="docs/react-redux/index.html">
            
                
                    <a href="../../../docs/react-redux/index.html">
                
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                            <b>9.</b>
                        
                        react-redux 文档
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="9.1" data-path="docs/react-redux/api.html">
            
                
                    <a href="../../../docs/react-redux/api.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>9.1.</b>
                        
                        API
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="9.2" data-path="docs/react-redux/troubleshooting.html">
            
                
                    <a href="../../../docs/react-redux/troubleshooting.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>9.2.</b>
                        
                        排错
                    </a>
            
            
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            </ul>
            
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                        <a id="edit-link" href="https://github.com/camsong/redux-in-chinese/tree/master/docs/recipes/reducers/InitializingState.md" class="btn fa fa-edit pull-left">&#xA0;&#xA0;&#x5F00;&#x59CB;&#x7EA0;&#x9519;</a><h1 id="%E5%88%9D%E5%A7%8B%E5%8C%96-state">&#x521D;&#x59CB;&#x5316; State</h1>
<p>&#x4E3B;&#x8981;&#x6709;&#x4E24;&#x79CD;&#x65B9;&#x6CD5;&#x6765;&#x521D;&#x59CB;&#x5316;&#x5E94;&#x7528;&#x7684; state &#x3002;</p>
<p>&#x53EF;&#x4EE5;&#x4F7F;&#x7528; <code>createStore</code> &#x65B9;&#x6CD5;&#x4E2D;&#x7684;&#x7B2C;&#x4E8C;&#x4E2A;&#x53EF;&#x9009;&#x53C2;&#x6570; <code>preloadedState</code>&#x3002;</p>
<p>&#x4E5F;&#x53EF;&#x4EE5;&#x5728; reducer &#x4E2D;&#x4E3A; <code>undefined</code> &#x7684; state &#x53C2;&#x6570;&#x6307;&#x5B9A;&#x7684;&#x9ED8;&#x8BA4;&#x7684;&#x521D;&#x59CB;&#x503C;&#x3002;&#x8FD9;&#x4E2A;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;&#x5728; reducer &#x4E2D;&#x6DFB;&#x52A0;&#x4E00;&#x4E2A;&#x660E;&#x786E;&#x7684;&#x68C0;&#x67E5;&#x6765;&#x5B8C;&#x6210;&#xFF0C;&#x4E5F;&#x53EF;&#x4EE5;&#x4F7F;&#x7528; ES6 &#x4E2D;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x7684;&#x8BED;&#x6CD5; <code><span class="token keyword">function</span> <span class="token function">myReducer</span><span class="token punctuation">(</span>state <span class="token operator">=</span> someDefaultValue<span class="token punctuation">,</span> action<span class="token punctuation">)</span></code></p>
<p>&#x8FD9;&#x4E24;&#x79CD;&#x65B9;&#x6CD5;&#x662F;&#x600E;&#x4E48;&#x76F8;&#x4E92;&#x5F71;&#x54CD;&#x7684;&#x4E5F;&#x8BB8;&#x5E76;&#x4E0D;&#x603B;&#x662F;&#x5F88;&#x6E05;&#x695A;&#xFF0C;&#x4E0D;&#x8FC7;&#x5E78;&#x8FD0;&#x7684;&#x662F;&#xFF0C;&#x8FD9;&#x4E2A;&#x8FC7;&#x7A0B;&#x9075;&#x5FAA;&#x7740;&#x4E00;&#x4E9B;&#x53EF;&#x9884;&#x89C1;&#x7684;&#x89C4;&#x5219;&#xFF0C;&#x8FD9;&#x91CC;&#x6765;&#x8BF4;&#x660E;&#x5B83;&#x4EEC;&#x662F;&#x5982;&#x4F55;&#x8054;&#x7CFB;&#x5728;&#x4E00;&#x8D77;&#x7684;&#x3002;</p>
<h2 id="%E6%A6%82%E8%A6%81">&#x6982;&#x8981;</h2>
<p>&#x5982;&#x679C;&#x4E0D;&#x4F7F;&#x7528; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x6216;&#x8005;&#x7C7B;&#x4F3C;&#x7684;&#x4EE3;&#x7801;&#xFF0C;&#x90A3;&#x4E48; <code>preloadedState</code> &#x603B;&#x662F;&#x4F1A;&#x4F18;&#x5148;&#x4E8E;&#x5728; reducer &#x91CC;&#x9762;&#x4F7F;&#x7528; <code>state <span class="token operator">=</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code> &#xFF0C;&#x56E0;&#x4E3A; <code>state</code> &#x4F20;&#x5230; reducer &#x91CC;&#x7684;<strong>&#x662F;</strong> <code>preloadedState</code> &#x7684; state <strong>&#x800C;&#x4E0D;&#x662F;</strong> <code>undefined</code>&#xFF0C;&#x6240;&#x4EE5; ES6 &#x7684;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x8BED;&#x6CD5;&#x5E76;&#x4E0D;&#x8D77;&#x4F5C;&#x7528;&#x3002;</p>
<p>&#x5982;&#x679C;&#x4F7F;&#x7528; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x65B9;&#x6CD5;&#xFF0C;&#x90A3;&#x4E48;&#x8FD9;&#x91CC;&#x7684;&#x884C;&#x4E3A;&#x5C31;&#x4F1A;&#x6709;&#x4E00;&#x4E9B;&#x7EC6;&#x5FAE;&#x7684;&#x5DEE;&#x522B;&#x4E86;&#x3002;&#x90A3;&#x4E9B;&#x6307;&#x5B9A;&#x4E86; <code>preloadedState</code> &#x7684; reducer &#x4F1A;&#x63A5;&#x6536;&#x5230;&#x90A3;&#x4E9B;&#x5BF9;&#x5E94;&#x7684; state&#x3002;&#x800C;&#x5176;&#x4ED6;&#x7684; reducer &#x5C06;&#x4F1A;&#x63A5;&#x6536;&#x5230; <code>undefined</code> &#x5E76;&#x56E0;&#x6B64;&#x56DE;&#x5230;&#x4E86; <code>state <span class="token operator">=</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code> &#x8FD9;&#x91CC;&#x53BB;&#x83B7;&#x53D6;&#x6307;&#x5B9A;&#x7684;&#x9ED8;&#x8BA4;&#x503C;&#x3002;</p>
<p><strong>&#x901A;&#x5E38;&#x60C5;&#x51B5;&#x4E0B;&#xFF0C;&#x901A;&#x8FC7; <code>preloadedState</code> &#x6307;&#x5B9A;&#x7684; state &#x8981;&#x4F18;&#x5148;&#x4E8E;&#x901A;&#x8FC7; reducer &#x6307;&#x5B9A; state&#x3002;&#x8FD9;&#x6837;&#x53EF;&#x4EE5;&#x4F7F;&#x901A;&#x8FC7; reducer &#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x6307;&#x5B9A;&#x521D;&#x59CB;&#x6570;&#x636E;&#x663E;&#x5F97;&#x66F4;&#x52A0;&#x7684;&#x5408;&#x7406;&#xFF0C;&#x5E76;&#x4E14;&#x5F53;&#x4F60;&#x4ECE;&#x4E00;&#x4E9B;&#x6301;&#x4E45;&#x5316;&#x7684;&#x5B58;&#x50A8;&#x5668;&#x6216;&#x670D;&#x52A1;&#x5668;&#x66F4;&#x65B0; store &#x7684;&#x65F6;&#x5019;&#xFF0C;&#x5141;&#x8BB8;&#x4F60;&#x66F4;&#x65B0;&#x5DF2;&#x5B58;&#x5728;&#x7684;&#x6570;&#x636E;&#xFF08;&#x5168;&#x90E8;&#x6216;&#x8005;&#x90E8;&#x5206;&#xFF09;&#x3002;</strong></p>
<h2 id="%E6%B7%B1%E5%BA%A6">&#x6DF1;&#x5EA6;</h2>
<h3 id="%E5%8D%95%E4%B8%80%E7%AE%80%E5%8D%95%E7%9A%84-reducer">&#x5355;&#x4E00;&#x7B80;&#x5355;&#x7684; Reducer</h3>
<p>&#x9996;&#x5148;&#xFF0C;&#x8BA9;&#x6211;&#x4EEC;&#x4E3E;&#x4E00;&#x4E2A;&#x5355;&#x72EC;&#x7684; reducer &#x7684;&#x4F8B;&#x5B50;&#xFF0C;&#x5E76;&#x4E14;&#x4E0D;&#x4F7F;&#x7528; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x65B9;&#x6CD5;&#x3002;</p>
<p>&#x90A3;&#x4E48;&#x4F60;&#x7684; reducer &#x53EF;&#x80FD;&#x50CF;&#x4E0B;&#x9762;&#x8FD9;&#x6837;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">counter</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">case</span> <span class="token string">&apos;INCREMENT&apos;</span><span class="token punctuation">:</span> <span class="token keyword">return</span> state <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
  <span class="token keyword">case</span> <span class="token string">&apos;DECREMENT&apos;</span><span class="token punctuation">:</span> <span class="token keyword">return</span> state <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">;</span>
  <span class="token keyword">default</span><span class="token punctuation">:</span> <span class="token keyword">return</span> state<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x8BA9;&#x6211;&#x4EEC;&#x521B;&#x5EFA;&#x4E00;&#x4E2A; store&#x3002;</p>
<pre><code><span class="token keyword">import</span> <span class="token punctuation">{</span> createStore <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> store <span class="token operator">=</span> <span class="token function">createStore</span><span class="token punctuation">(</span>counter<span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>store<span class="token punctuation">.</span><span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment" spellcheck="true">// 0</span>
</code></pre><p>&#x521D;&#x59CB;&#x7684;&#x72B6;&#x6001;&#x662F; 0 &#x3002;&#x4E3A;&#x4EC0;&#x4E48;&#x5462;&#xFF1F;&#x56E0;&#x4E3A; <code>createStore</code> &#x7684;&#x7B2C;&#x4E8C;&#x4E2A;&#x53C2;&#x6570;&#x662F; <code>undefined</code>&#x3002;&#x8FD9;&#x662F; <code>state</code> &#x7B2C;&#x4E00;&#x6B21;&#x4F20;&#x5230;&#x4E86; reducer &#x5F53;&#x4E2D;&#x3002;Redux &#x4F1A;&#x53D1;&#x8D77;&#xFF08;dispatch&#xFF09;&#x4E00;&#x4E2A;&#x201C;&#x865A;&#x62DF;&#x201D;&#x7684; action &#x6765;&#x586B;&#x5145;&#x8FD9;&#x4E2A; state &#x3002;&#x6240;&#x4EE5; <code>counter</code> reducer &#x91CC;&#x83B7;&#x5F97;&#x7684; <code>state</code> &#x7B49;&#x4E8E; <code>undefined</code>&#x3002;<strong>&#x5B9E;&#x9645;&#x4E0A;&#x8FD9;&#x76F8;&#x5F53;&#x4E8E;&#x89E6;&#x53D1;&#x4E86;&#x90A3;&#x4E2A;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x7684;&#x7279;&#x6027;</strong>&#x3002;&#x56E0;&#x6B64;&#xFF0C;&#x73B0;&#x5728; <code>state</code> &#x7684;&#x503C;&#x662F;&#x8BBE;&#x5B9A;&#x7684;&#x9ED8;&#x8BA4;&#x53C2;&#x6570; <code><span class="token number">0</span></code> &#xFF0C;&#x8FD9;&#x4E2A; state (<code><span class="token number">0</span></code>) &#x662F;&#x8FD9;&#x91CC; reducer &#x7684;&#x8FD4;&#x56DE;&#x503C;&#x3002;</p>
<p>&#x63A5;&#x4E0B;&#x6765;&#x8BA9;&#x6211;&#x4EEC;&#x4E3E;&#x4E00;&#x4E2A;&#x4E0D;&#x540C;&#x573A;&#x666F;&#x7684;&#x4F8B;&#x5B50;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> createStore <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> store <span class="token operator">=</span> <span class="token function">createStore</span><span class="token punctuation">(</span>counter<span class="token punctuation">,</span> <span class="token number">42</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>store<span class="token punctuation">.</span><span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment" spellcheck="true">// 42</span>
</code></pre>
<p>&#x4E3A;&#x4EC0;&#x4E48;&#x8FD9;&#x6B21;&#x8FD9;&#x91CC;&#x7684;&#x503C;&#x662F; <code><span class="token number">42</span></code> &#x800C;&#x4E0D;&#x662F; <code><span class="token number">0</span></code> &#x5462;&#xFF1F;&#x56E0;&#x4E3A; <code>createStore</code> &#x7684;&#x7B2C;&#x4E8C;&#x4E2A;&#x53C2;&#x6570;&#x662F; <code><span class="token number">42</span></code> &#x3002;&#x8FD9;&#x4E2A;&#x53C2;&#x6570;&#x4F1A;&#x8D4B;&#x7ED9; state &#x5E76;&#x4F34;&#x968F;&#x7740;&#x4E00;&#x4E2A;&#x865A;&#x62DF; action &#x4E00;&#x8D77;&#x4F20;&#x7ED9; reducer&#x3002;<strong>&#x8FD9;&#x6B21;&#xFF0C;&#x4F20;&#x7ED9; reducer &#x7684; <code>state</code> &#x4E0D;&#x518D;&#x662F; <code>undefined</code> (&#x662F; <code><span class="token number">42</span></code> )&#xFF0C;&#x6240;&#x4EE5; ES6 &#x7684;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x7279;&#x6027;&#x6CA1;&#x6709;&#x8D77;&#x4F5C;&#x7528;&#x3002;</strong>&#x6240;&#x4EE5;&#x8FD9;&#x91CC;&#x7684; <code>state</code> &#x662F; <code><span class="token number">42</span></code>&#xFF0C;<code><span class="token number">42</span></code> &#x662F;&#x8FD9;&#x4E2A; reducer &#x7684;&#x8FD4;&#x56DE;&#x503C;&#x3002;</p>
<h3 id="%E7%BB%84%E5%90%88%E5%A4%9A%E4%B8%AA-reducers">&#x7EC4;&#x5408;&#x591A;&#x4E2A; Reducers</h3>
<p>&#x73B0;&#x5728;&#x8BA9;&#x6211;&#x4EEC;&#x4E3E;&#x4E00;&#x4E2A;&#x4F7F;&#x7528; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<p>&#x4F60;&#x6709;&#x4E24;&#x4E2A; reducers&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">a</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token string">&apos;lol&apos;</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> state<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">b</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token string">&apos;wat&apos;</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> state<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x8FD9;&#x4E2A;&#x7EC4;&#x5408;&#x7684; reducer &#x901A;&#x8FC7; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">{</span> a<span class="token punctuation">,</span> b <span class="token punctuation">}</span><span class="token punctuation">)</span></code> &#x751F;&#x6210;&#xFF0C;&#x5C31;&#x50CF;&#x4E0B;&#x9762;&#x8FD9;&#x6837;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token comment" spellcheck="true">// const combined = combineReducers({ a, b })</span>
<span class="token keyword">function</span> <span class="token function">combined</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">{</span>
    a<span class="token punctuation">:</span> <span class="token function">a</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>a<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    b<span class="token punctuation">:</span> <span class="token function">b</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>b<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
  <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x5982;&#x679C;&#x6211;&#x4EEC;&#x8C03;&#x7528; <code>createStore</code> &#x65B9;&#x6CD5;&#x5E76;&#x4E14;&#x4E0D;&#x4F7F;&#x7528; <code>preloadedState</code> &#x53C2;&#x6570;&#xFF0C;&#x5B83;&#x5C06;&#x4F1A;&#x628A; <code>state</code> &#x521D;&#x59CB;&#x5316;&#x6210; <code><span class="token punctuation">{</span><span class="token punctuation">}</span></code>&#x3002; &#x56E0;&#x6B64;&#xFF0C;&#x4F20;&#x5165; reducer &#x7684;<code>state<span class="token punctuation">.</span>a</code> &#x548C; <code>state<span class="token punctuation">.</span>b</code> &#x7684;&#x503C;&#x5C06;&#x4F1A;&#x662F; <code>undefined</code> **&#x4E0D;&#x8BBA;&#x662F; <code>a</code> &#x8FD8;&#x662F; <code>b</code> &#x7684;&#x503C;&#x90FD;&#x662F; <code>undefined</code> &#xFF0C;&#x8FD9;&#x65F6;&#x5982;&#x679C;&#x6307;&#x5B9A; <code>state</code> &#x7684;&#x9ED8;&#x8BA4;&#x503C;&#xFF0C;&#x90A3;&#x4E48; reducer &#x5C06;&#x4F1A;&#x8FD4;&#x56DE;&#x8FD9;&#x4E2A;&#x9ED8;&#x8BA4;&#x503C;&#x3002; &#x8FD9;&#x5C31;&#x662F;&#x7B2C;&#x4E00;&#x6B21;&#x8BF7;&#x6C42;&#x8FD9;&#x4E2A;&#x7EC4;&#x5408;&#x7684; reducer &#x65F6;&#x8FD4;&#x56DE; state <code><span class="token punctuation">{</span> a<span class="token punctuation">:</span> <span class="token string">&apos;lol&apos;</span><span class="token punctuation">,</span> b<span class="token punctuation">:</span> <span class="token string">&apos;wat&apos;</span><span class="token punctuation">}</span></code> &#x7684;&#x539F;&#x56E0;&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> createStore <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> store <span class="token operator">=</span> <span class="token function">createStore</span><span class="token punctuation">(</span>combined<span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>store<span class="token punctuation">.</span><span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment" spellcheck="true">// { a: &apos;lol&apos;, b: &apos;wat&apos; }</span>
</code></pre>
<p>&#x63A5;&#x4E0B;&#x6765;&#x8BA9;&#x6211;&#x4EEC;&#x4E3E;&#x4E00;&#x4E2A;&#x4E0D;&#x540C;&#x7684;&#x573A;&#x666F;&#x7684;&#x4F8B;&#x5B50;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> createStore <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> store <span class="token operator">=</span> <span class="token function">createStore</span><span class="token punctuation">(</span>combined<span class="token punctuation">,</span> <span class="token punctuation">{</span> a<span class="token punctuation">:</span> <span class="token string">&apos;horse&apos;</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>store<span class="token punctuation">.</span><span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment" spellcheck="true">// { a: &apos;horse&apos;, b: &apos;wat&apos; }</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x6307;&#x5B9A;&#x4E86; <code><span class="token function">createStore</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x7684; <code>preloadedState</code> &#x53C2;&#x6570;&#x3002;&#x73B0;&#x5728;&#x8FD9;&#x4E2A;&#x7EC4;&#x5408;&#x7684; reducer &#x8FD4;&#x56DE;&#x7684; state &#x7ED3;&#x5408;&#x4E86;&#x6211;&#x4EEC;&#x6307;&#x5B9A;&#x7ED9; <code>a</code> &#x7684;&#x9ED8;&#x8BA4;&#x503C; <code>horse</code> &#x4EE5;&#x53CA;&#x901A;&#x8FC7; reducer &#x672C;&#x8EAB;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x6307;&#x5B9A;&#x7684; <code>b</code> &#x7684;&#x503C; <code><span class="token string">&apos;wat&apos;</span></code> &#x3002;</p>
<p>&#x8BA9;&#x6211;&#x4EEC;&#x91CD;&#x65B0;&#x770B;&#x770B;&#x8FD9;&#x4E2A;&#x7EC4;&#x5408;&#x7684; reducer &#x505A;&#x4E86;&#x4EC0;&#x4E48;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token comment" spellcheck="true">// const combined = combineReducers({ a, b })</span>
<span class="token keyword">function</span> <span class="token function">combined</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">{</span>
    a<span class="token punctuation">:</span> <span class="token function">a</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>a<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    b<span class="token punctuation">:</span> <span class="token function">b</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>b<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
  <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x5728;&#x8FD9;&#x4E2A;&#x6848;&#x4F8B;&#x4E2D;&#xFF0C;<code>state</code> &#x662F;&#x6211;&#x4EEC;&#x6307;&#x5B9A;&#x7684;&#xFF0C;&#x6240;&#x4EE5;&#x5B83;&#x5E76;&#x6CA1;&#x6709;&#x88AB;&#x8D4B;&#x503C;&#x4E3A; <code><span class="token punctuation">{</span><span class="token punctuation">}</span></code>&#x3002;&#x8FD9;&#x662F;&#x4E00;&#x4E2A; <code>a</code> &#x7684;&#x503C;&#x662F; <code><span class="token string">&apos;horse&apos;</span></code> &#x7684;&#x5BF9;&#x8C61;&#xFF0C;&#x4F46;&#x662F;&#x6CA1;&#x6709; <code>b</code> &#x7684;&#x503C;&#x3002;&#x8FD9;&#x5C31;&#x662F;&#x4E3A;&#x4EC0;&#x4E48; <code>a</code> reducer &#x6536;&#x5230;&#x4E86; <code><span class="token string">&apos;horse&apos;</span></code> &#x7684; state &#x5E76;&#x9AD8;&#x5174;&#x5730;&#x8FD4;&#x56DE;&#x5B83;&#xFF0C;&#x4F46; <code>b</code> reducer &#x5374;&#x5F97;&#x5230;&#x4E86; <code>undefined</code> state &#x5E76;&#x56E0;&#x6B64;&#x8FD4;&#x56DE;&#x4E86;&#x5B83;&#x81EA;&#x5DF1;&#x8BBE;&#x5B9A;&#x7684;&#x9ED8;&#x8BA4;&#x503C;&#xFF08;&#x5728;&#x8FD9;&#x4E2A;&#x4F8B;&#x5B50;&#x91CC;&#x662F;<code><span class="token string">&apos;wat&apos;</span></code>&#xFF09;&#x3002;&#x8FD9;&#x5C31;&#x662F;&#x6211;&#x4EEC;&#x5982;&#x4F55;&#x5F97;&#x5230;&#x7684; <code><span class="token punctuation">{</span> a<span class="token punctuation">:</span> <span class="token string">&apos;horse&apos;</span><span class="token punctuation">,</span> b<span class="token punctuation">:</span> <span class="token string">&apos;wat&apos;</span> <span class="token punctuation">}</span></code> &#x8FD9;&#x4E2A;&#x7ED3;&#x679C;&#x3002;</p>
<h2 id="%E6%80%BB%E7%BB%93">&#x603B;&#x7ED3;</h2>
<p>&#x7EFC;&#x4E0A;&#x6240;&#x8FF0;&#xFF0C;&#x5982;&#x679C;&#x4F60;&#x9075;&#x5B88; Redux &#x7684;&#x7EA6;&#x5B9A;&#x5E76;&#x4E14;&#x8981;&#x8BA9; reducer &#x4E2D; <code>undefined</code> &#x7684; <code>state</code> &#x53C2;&#x6570;&#x8FD4;&#x56DE;&#x521D;&#x59CB; state &#xFF08;&#x6700;&#x7B80;&#x5355;&#x7684;&#x5B9E;&#x73B0;&#x65B9;&#x6CD5;&#x5C31;&#x662F;&#x5229;&#x7528; ES6 &#x7684;&#x9ED8;&#x8BA4;&#x53C2;&#x6570;&#x6765;&#x6307;&#x5B9A; state&#xFF09;&#xFF0C;&#x90A3;&#x4E48;&#x5BF9;&#x4E8E;&#x7EC4;&#x5408;&#x591A;&#x4E2A; reducers &#x7684;&#x60C5;&#x51B5;&#xFF0C;&#x8FD9;&#x5C06;&#x662F;&#x4E00;&#x4E2A;&#x5F88;&#x6709;&#x7528;&#x7684;&#x505A;&#x6CD5;&#xFF0C;<strong>&#x4ED6;&#x4EEC;&#x4F1A;&#x4F18;&#x5148;&#x9009;&#x62E9;&#x901A;&#x8FC7; <code>preloadedState</code> &#x53C2;&#x6570;&#x4F20;&#x5230; <code><span class="token function">createStore</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x7684;&#x5BF9;&#x8C61;&#x4E2D;&#x7684;&#x76F8;&#x5E94;&#x503C;&#xFF0C;&#x4F46;&#x662F;&#x5982;&#x679C;&#x4F60;&#x4E0D;&#x4F20;&#x4EFB;&#x4F55;&#x4E1C;&#x897F;&#xFF0C;&#x6216;&#x8005;&#x6CA1;&#x8BBE;&#x7F6E;&#x76F8;&#x5E94;&#x7684;&#x5B57;&#x6BB5;&#xFF0C;&#x90A3;&#x4E48; reducer &#x5C31;&#x4F1A;&#x9009;&#x62E9;&#x6307;&#x5B9A;&#x7684;&#x9ED8;&#x8BA4; <code>state</code> &#x53C2;&#x6570;&#x6765;&#x53D6;&#x4EE3;</strong>&#x3002;&#x8FD9;&#x6837;&#x7684;&#x65B9;&#x6CD5;&#x6548;&#x679C;&#x5F88;&#x597D;&#xFF0C;&#x56E0;&#x4E3A;&#x4ED6;&#x65E2;&#x80FD;&#x7528;&#x6765;&#x521D;&#x59CB;&#x5316;&#x4E5F;&#x53EF;&#x4EE5;&#x7528;&#x6765;&#x66F4;&#x65B0;&#x73B0;&#x6709;&#x7684;&#x6570;&#x636E;&#xFF0C;&#x4E0D;&#x8FC7;&#x5982;&#x679C;&#x6570;&#x636E;&#x6CA1;&#x6709;&#x4FDD;&#x62A4;&#x63AA;&#x65BD;&#x7684;&#x8BDD;&#xFF0C;&#x8FD9;&#x6837;&#x505A;&#x4E5F;&#x4F1A;&#x4F7F;&#x4E00;&#x4E9B;&#x72EC;&#x7ACB;&#x7684; reducer &#x7684; state &#x88AB;&#x91CD;&#x65B0;&#x8D4B;&#x503C;&#x3002;&#x5F53;&#x7136;&#x4F60;&#x53EF;&#x4EE5;&#x9012;&#x5F52;&#x5730;&#x4F7F;&#x7528;&#x8FD9;&#x4E2A;&#x6A21;&#x5F0F;&#xFF0C;&#x6BD4;&#x5982;&#x4F60;&#x53EF;&#x4EE5;&#x5728;&#x591A;&#x4E2A;&#x5C42;&#x7EA7;&#x4E0A;&#x4F7F;&#x7528; <code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x65B9;&#x6CD5;&#xFF0C;&#x6216;&#x8005;&#x751A;&#x81F3;&#x624B;&#x52A8;&#x7684;&#x7EC4;&#x5408;&#x8FD9;&#x4E9B; reducer &#x5E76;&#x4E14;&#x4F20;&#x5165;&#x5BF9;&#x5E94;&#x90E8;&#x5206;&#x7684; state tree&#x3002;</p>

                    
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